In the field of vacuum filter bags there has recently been a trend towards longer service life. Thus, the current vacuum filter bags are capable of holding much more dust than previously before the bag is completely filled and as such to be replaced. Such vacuum filter bags are, for example, described in EP-A-1 254 693 and EP-A-1 258 277. Since these types of vacuum filter bags, due to their higher dust holding capacity, must be replaced less frequently, the bags remain in the vacuum cleaner for a longer period of time. Consequently, more malodors are generated in the bags.
The malodors are due to the presence of organic materials such as pet hairs, and microorganisms, such as bacteria, mold, or mites, which are soaked up in addition to mineral dust particles upon vacuuming. Through the decomposition of the organic materials being favored by the presence of humidity, malodors are generated which will accumulate in the dust compartment. If the vacuum cleaner is switched on after standing for a longer time, these malodors are blown out all at once. Most users find these malodors unpleasant and unhygienic.
It is known to equip vacuum cleaners with separate odor filters with the purpose of absorbing malodors.
These odor filters usually contain active carbon and are arranged downstream of the filter bag and the turbine as a separate filter unit, e.g., a filter cassette. Such odor filter units are known, e.g., from DE-A-42 40 172 and DE-A-42 04 553. Using such filter cassettes has the drawback that the vacuum cleaner must be specifically constructed to allow their use. Alternative odor filters arranged downstream of the vacuum filter bag and upstream of the turbine are disclosed in DE-A-195 13 658.
Separate filter units will generate additional filter resistance with a concomitant reduced airflow rate. Consequently, separate odor filter units such as filter cassettes are detrimental to high airflow rate and service life of the vacuum filter bag. Furthermore, the odor filter cassettes are arranged distant from the place where the malodors are generated. As such they may not retain the malodors being emitted when the vacuum cleaner is not in use. When the vacuum cleaner is switched on, all malodors generated in the time since its last use have to be retained at once i.e. shock-wise. This is usually accomplished only insufficiently. The insufficient absorption of malodors is due to the short residence time resulting from the high air velocity of about 1.8 m/s in a standard vacuum cleaner. The absorption efficiency is strongly dependent on the residence time of the odor components in the absorption medium. In the separate odor filter units of the prior art, the odor components contained in the air flow do not stay long enough in contact with the active carbon to be absorbed to a sufficient degree. In addition, the user has no possibility to check whether the separate downstream odor filter is depleted already and cannot absorb malodors any longer. Consequently, the filter is either replaced too early i.e. when this has significant absorption capacity left, which is detrimental from an economical point of view, or too late i.e. when malodors are discernable already.
The idea of absorbing malodors immediately upon their formation by providing the dust filter bag as such with odor absorbing materials is generally addressed in DE-A-195 31 343.
In view of the above drawbacks of separate odor filters, DE 19 615 209 C1 proposes a vacuum filter bag consisting of at least two layers wherein the upstream layer consists of filter paper provided with adsorber particles such as carbon or natural or synthetic zeolites. The second layer arranged on the downstream side is a covering layer with particle filter properties. The adsorber particles are in close proximity of the place of malodor generation and are described to achieve, as such, a good odor removal through the longer contact time of odor component and adsorber particles. Since the adsorber particles are incorporated into the vacuum filter bag, these will be replaced simultaneously with the dust removal filter unit which makes the handling more convenient than in filter systems with separate odor filter units.
However, the vacuum filter bags of DE 19 615 209 C1 are still unsatisfactory.
According to DE 19 615 209 C1, the adsorber particles may be introduced into the filter paper by way of impregnation. In the alternative, it is possible to cover at least one side of the filter paper that contains adsorber particles. No detailed description on how the adsorber particles are introduced into the filter paper is given. Evidently, they are only weakly fixed to the filter paper and a substantial proportion of them will be released by the air flowing through the filter upon use in a vacuum cleaner. Otherwise, the protection of the adsorber particles against abrasion and loss by means of the covering layer on the downstream side would not be necessary. The covering layer will capture adsorber particles released from the filter paper. As such, the released particles captured in the covering layer will contribute to the overall filter resistance by bag clogging. In addition, the capability of the particles to absorb odor components may be deteriorated or even be lost completely when released from the filter paper. Due to the abrasion of the odor-retaining particles, the odor absorption of the vacuum cleaner bag of the above patent may therefore decrease with time and can be expected to be low towards the end of a lifetime of the vacuum filter bag. Moreover, this vacuum filter bag requires the presence of at least two layers, and each layer will contribute to the overall filter resistance and bag clogging. Hence, the vacuum filter bag of DE 19 615 209 C1 is still not satisfactory with respect to the service life of the filter bag, both in terms of the malodor absorption and the dust holding capability.
WO 00/40134 describes a multi-layer vacuum filter bag comprising a layer of adsorption material such as active carbon or zeolites. Thereby, the adsorption material may be arranged loosely between two other layers or may be incorporated into a carrier material such as porous foam, reticulated foam, or a non-woven. WO 00/40134 does not describe how the absorption material is incorporated into the carrier. Using loose adsorption material may cause problems upon bag manufacturing. For instance, the material may get lost at the cutting edges upon cutting the web and punching the in-flow opening. This may lead to contamination of the manufacturing machines, giving rise to failures in the bag manufacturing process.